Image reading device and image reading method

ABSTRACT

An image reading device includes a tray, a paper feed roller that conveys a sheet, a first sensor that detects a front end and a rear end of the sheet, a second sensor that detects the front end of the sheet, and a scanner that reads an image on a front side of the sheet and reads an image on a back side of the sheet. A controller determines a first time duration that elapses from the detection of the front end of the sheet by the first sensor to the detection of the rear end of the sheet by the first sensor and operates the scanner to read the image on the back side of the sheet over a second time duration equal in length to the first time duration. The second time duration begins after the front end of the sheet is detected by the second sensor.

FIELD

Embodiments described herein relate generally to an image reading deviceand an image reading method.

BACKGROUND

In the related art, when reading a sheet with an image reading device,the sheet is read according to the sheet size. However, when copying byspecifying a magnification or reading a sheet of a size different from astandard size, the reading extends beyond the length of the sheet, suchthat a shadow at the rear end of the sheet is read and the imageincludes streaks. In order to remove these streaks, if the rear end ofthe sheet is detected by the image reading device, the streaks on therear end of the sheet are removed by forcibly masking the image data towhite from the front of the rear end portion to be read.

In the image reading device of the related art, the front end and therear end of the sheet are detected by a sensor, the reading of the sheetis started by the detection of the front end, and the masking of theread image is started by the detection of the rear end. However, afterthe sheet passes through a front-side reading roller, the behavior ofthe rear end of the sheet becomes unstable, and the rear end of thesheet on the back side cannot be detected correctly. In this case, therear end streaks could not be removed, or the image was removed in somecases.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an example of an overallconfiguration of an image forming apparatus of an embodiment;

FIG. 2 is a side section view illustrating an internal configuration ofan image reading device;

FIG. 3 is a block diagram illustrating a functional configuration of theimage forming apparatus; and

FIG. 4 is a timing chart illustrating a processing flow of the imageforming apparatus.

DETAILED DESCRIPTION

In general, according to at least one embodiment, an image readingdevice includes a tray, a paper feed roller, a first sensor, a secondsensor, a scanner, and a controller. The tray supports a sheet. Thepaper feed roller conveys the sheet away from the tray. The first sensoris positioned to detect the front end and the rear end of the sheet asthe sheet is conveyed. The second sensor is positioned to detect thefront end of the sheet as the sheet is conveyed. The scanner isconfigured to read an image on the front side of the sheet at afront-side reading position, and read an image on the back side of thesheet at a back-side reading position. The controller is configured todetermine a first time duration that elapses from the detection of thefront end of the sheet by the first sensor to the detection of the rearend of the sheet by the first sensor and operate the scanner to read theimage on the back side of the sheet over a second time duration equal inlength to the first time duration. The second time duration begins at afirst point in time after the front end of the sheet is detected by thesecond sensor and ends at a second point in time.

Hereinafter, the image reading device and the image reading method of atleast one embodiment will be described with reference to drawings.

FIG. 1 is a perspective view illustrating an example of an overallconfiguration of an image forming apparatus 100 of at least oneembodiment. The image forming apparatus 100 of at least one embodimentis a multifunction peripheral (MFP) capable of forming a toner image ona sheet. The sheet is, for example, paper on which characters or imagesare formed. The sheet may be any material as long as the image formingapparatus 100 can form an image thereon. The image forming apparatus 100reads an image appearing on a sheet, generates digital data, andgenerates image information.

The image forming apparatus 100 executes printing by image formingprocessing and image fixing processing. The image forming processing isprocessing of forming an image on a sheet. The image fixing processingis processing of fixing an image formed on a sheet on the sheet. Theimage forming apparatus 100 is an aspect of the image reading apparatus.

The image forming apparatus 100 includes a display 110, a control panel120, a printer unit 130, a sheet accommodating unit 140, and an imagereading device 150. The display 110 (e.g., an output device) is an imagedisplay device such as a liquid crystal display, an organic electroluminescence (EL) display, or the like. The display 110 displays variousinformation related to the image forming apparatus 100. The display 110outputs a signal corresponding to the operation performed by a user tothe control unit of the image forming apparatus 100. In the followingdescription, the control unit of the image forming apparatus 100 is acontrol unit different from the control unit included in the imagereading device 150. The display 110 accepts user operations (e.g., actsas an input device).

The control panel 120 includes an operation unit. The operation unitincludes a plurality of buttons and the like. The operation unitreceives a user operation (e.g., acts as an input device). For example,the operation unit receives a print instruction and an instruction forenabling or disabling mask processing. The mask processing is processingof converting at least a part of image data into a white image. Theoperation unit outputs a signal corresponding to the operation performedby the user to the internal control unit. The display 110 and thecontrol panel 120 may be configured as an integral touch panel (e.g.,the display 110 and the control panel 120 may act as a user interface oran operator interface).

The printer unit 130 (e.g., a printer) executes image forming processingand image fixing processing. Specifically, the printer unit 130 forms animage on a sheet based on the image information generated by the imagereading device 150 or the image information received via a communicationpath. For example, the printer unit 130 forms a toner image on a sheetwhose front end is aligned by a registration roller 40. The printer unit130 heats and pressurizes the sheet to fix an image (for example, atoner image) formed on the sheet.

The sheet accommodating unit 140 (e.g., a sheet feeder) includes asingle or a plurality of paper feed cassettes. Each of the paper feedcassettes stores a predetermined size and a predetermined type of sheet.The predetermined type of sheet is a sheet having a different thickness.For example, the predetermined type of sheet includes plain paper, thickpaper, and the like.

The image reading device 150 (e.g., a scanner) reads the imageinformation to be read as light brightness. For example, the imagereading device 150 reads the image information printed on the sheet tobe read set in the own device. For example, the image reading device 150reads the image information on the front side printed on the sheet andthe image information on the back side. The image reading device 150records the read image information on the front side and the imageinformation on the back side. The recorded image information may betransmitted to another information processing apparatus via a network(e.g., a local area network, the Internet, etc.). The recorded imageinformation may be formed on the sheet by the printer unit 130. Theimage reading device 150 is, for example, an auto document feeder (ADF).

FIG. 2 is a side section view illustrating an internal configuration ofthe image reading device 150 of at least one embodiment. FIG. 2illustrates only the configuration necessary for illustrating theprocessing of the image reading device 150 in the present embodiment.

The image reading device 150 includes a mounting unit 151, a sheetlength sensor 152, a sheet length sensor 153, a sheet width sensor 154,a pickup roller 155, a separation roller 156, a paper feed roller 157, afront-side reading start sensor 158, a roller 159, a back-side readingstart sensor 160, a front-side image reading unit 161, a roller 162, aback-side image reading unit 163, and a control unit 164. In FIG. 2 ,the arrow 1 indicates the direction in which a sheet is conveyed.

The mounting unit 151 (e.g., a sheet support) is a tray on which a sheetis mounted. The sheet length sensor 152 detects the sheet mounted on themounting unit 151. The sheet length sensor 153 detects the sheet mountedon the mounting unit 151. The sheet length sensors 152 and 153 are usedto detect the length of the sheet mounted on the mounting unit 151. Thesheet width sensor 154 detects the sheet mounted on the mounting unit151. The sheet width sensor 154 is used to detect the width of the sheetmounted on the mounting unit 151. The size of the sheet mounted on themounting unit 151 is determined by the detection results of the sheetlength sensors 152 and 153, and the sheet width sensor 154.

The pickup roller 155 picks up the sheets mounted on the mounting unit151 one by one (e.g., individually).

The separation roller 156 is a roller for separating the sheets in orderto convey the sheets mounted on the mounting unit 151 one by one. Thepaper feed roller 157 feeds the sheet mounted on the mounting unit 151.The separation roller 156 and the paper feed roller 157 rotate inopposite directions. The paper feed roller 157 feeds the sheet picked upby the pickup roller 155 to the downstream side. The downstream side isthe direction in which the sheet is conveyed (for example, the directionindicated by the arrow 1).

The front-side reading start sensor 158 is provided on the downstreamside of the paper feed roller 157. The front-side reading start sensor158 detects the sheet fed by the paper feed roller 157. For example, thefront-side reading start sensor 158 detects the front end and the rearend of the sheet fed by the paper feed roller 157. The front-sidereading start sensor 158 is provided to detect the sheet before thefront side of the sheet is read. The front-side reading start sensor 158is an optical sensor. By way of example, the front-side reading startsensor 158 may include a break beam sensor that activates in response toan object (e.g., the sheet) interrupting a beam of light. The front-sidereading start sensor 158 is one aspect of the first sensor. Thefront-side reading start sensor 158 notifies the control unit 164 of thedetection result.

The roller 159 is provided on the downstream side of the front-sidereading start sensor 158 and on the upstream side of a front-sidereading position FRP. The roller 159 sends the sheet that has passedthrough the front-side reading start sensor 158 to the front-sidereading position FRP.

The back-side reading start sensor 160 is provided on the downstreamside of the front-side reading start sensor 158. The back-side readingstart sensor 160 detects the sheet conveyed by the roller 159. Forexample, the back-side reading start sensor 160 detects the front end ofthe sheet that has passed through the front-side reading start sensor158. The back-side reading start sensor 160 is provided to detect thesheet before the back side of the sheet is read. The back-side readingstart sensor 160 is a sensor with an actuator. More specifically, theback-side reading start sensor 160 is a sensor capable of detecting thesheet in response to the sheet contacting and driving movement of amovable portion of the actuator. It is difficult to install an opticalsensor in the place where the back-side reading start sensor 160 isinstalled due to the size problem (e.g., an optical sensor is difficultto package between the roller 159 and the roller 162 due to sizeconstraints). Therefore, instead of the optical sensor, a sensor with anactuator is used for the back-side reading start sensor 160. Theback-side reading start sensor 160 is one aspect of the second sensor.The back-side reading start sensor 160 notifies the control unit 164 ofthe detection result.

The front-side image reading unit 161 reads an image on the front sideof the sheet.

The roller 162 is provided on the downstream side of the back-sidereading start sensor 160 and on the upstream side of a back-side readingposition BRP. The roller 162 conveys the sheet that has passed throughthe back-side reading start sensor 160 to the back-side reading positionBRP.

The back-side image reading unit 163 reads the image on the back side ofthe sheet (e.g., a side of the sheet opposite the front side).

The control unit 164 (e.g., a controller) controls the operation of theimage reading device 150. Here, an example of the processing of thecontrol unit 164 will be described. If the control unit 164 detects thatthe sheet is placed on the mounting unit 151 (e.g., by an originalpresence and absence sensor), the control unit 164 notifies the controlunit provided in the image forming apparatus 100 that there is a sheet.The control unit 164 controls the drive of each roller (for example,pickup roller 155, separation roller 156, paper feed roller 157, roller159, roller 162, and the like) included in the image reading device 150.By way of example, the control unit 164 may activate, vary the speed of,or deactivate one or more actuators (e.g., electric motors) that driveeach roller.

The control unit 164 performs control according to the detection resultof the front-side reading start sensor 158 or the back-side readingstart sensor 160. The control unit 164 has a front-side reading starttimer, a front-side reading end timer, a sheet length measurement timer,and a back-side reading start timer. The front-side reading start timer,the front-side reading end timer, the sheet length measurement timer,and the back-side reading start timer are timers realized by software(e.g., within the control unit 164).

The front-side reading start timer is a timer of which a reference timefor starting the reading of the front side of the sheet is set. The timein the front-side reading start timer is set as the conveyance timecalculated based on the conveyance distance from the position where thefront-side reading start sensor 158 is activated or turned on (e.g., inresponse to the sheet passing near the front-side reading start sensor)to the front-side reading position FRP and the conveyance speed of thesheet. Hereinafter, the conveyance distance from the position where thefront-side reading start sensor 158 is turned on to the front-sidereading position FRP is referred to as a first conveyance distance. Theconveyance time calculated based on the first conveyance distance isdescribed as a first conveyance time.

When the time set in the front-side reading start timer has elapsed, thecontrol unit 164 notifies the control unit of the image formingapparatus 100 of an instruction (hereinafter, referred to as “front-sidereading signal”) to turn on a front-side sub-scanned image enabledsignal in order to start reading the front side of the sheet. Thefront-side sub-scanned image enabled signal is a signal for starting toread an image in the sub-scan direction of the front side of the sheet.Turning on the front-side sub-scanned image enabled signal meansstarting to read the image in the sub-scan direction.

The front-side reading end timer is a timer of which a reference timefor ending the reading of the front side of the sheet is set. The timein the front-side reading end timer is set as the conveyance timecalculated based on the distance obtained by subtracting the value ofthe cut mount of the rear end streaks, which is obtained in advance,from the first conveyance distance. The cut amount is adjustable.

The control unit 164 sets to mask the image data on the front side whenthe time set in the front-side reading end timer elapses. For example,the control unit 164 performs mask processing on the image data afterthe lapse of time set in the front-side reading end timer.

The sheet length measurement timer is a timer for measuring the lengthof the sheet. The sheet length measurement timer starts counting at thetiming (i.e., the point in time) when the front end of the sheet isdetected by the front-side reading start sensor 158, and stops countingat the timing when the rear end of the sheet is detected by thefront-side reading start sensor 158. The length of the sheet can bemeasured based on the time from the timing when the front end of thesheet is detected by the front-side reading start sensor 158 to thedetection of the rear end of the sheet.

The back-side reading start timer is a timer of which a reference timefor starting the reading of the back side of the sheet is set. The timein the back-side reading start timer is set as the conveyance timecalculated based on the conveyance distance from the position where theback-side reading start sensor 160 is turned on to the back-side readingposition BRP and the conveyance speed of the sheet. Hereinafter, theconveyance distance from the position where the back-side reading startsensor 160 is turned on to the back-side reading position BRP isreferred to as a second conveyance distance. The conveyance timecalculated based on the second conveyance distance is described as asecond conveyance time.

When the time set in the back-side reading start timer has elapsed, thecontrol unit 164 notifies the control unit of the image formingapparatus 100 of an instruction (hereinafter, referred to as “back-sidereading signal”) to turn on a back-side sub-scanned image enabled signalin order to start reading the back side of the sheet. The back-sidesub-scanned image enabled signal is a signal for starting to read animage in the sub-scan direction of the back side of the sheet. Turningon the back-side sub-scanned image enabled signal means starting to readthe image in the sub-scan direction.

The control unit 164 notifies the control unit of the image formingapparatus 100 of the sheet size when the scan is started. The controlunit 164 acquires magnification information, the number of readinglines, double-sided reading information, and information regarding thepresence or absence of the rear end streak cut from the control unit ofthe image forming apparatus 100. The magnification information isinformation indicating the magnification when printing the sheet. Thenumber of reading lines indicates the number of read lines on the sheet.The double-sided reading information is information indicating aninstruction for double-sided reading. The information regarding thepresence or absence of the rear end streak cut is information indicatingwhether the mask processing is enabled or disabled. If the rear endstreak cut is enabled, it indicates that the mask processing is enabled.If the rear end streak cut is disabled, it indicates that the maskprocessing is disabled.

FIG. 3 is a block diagram illustrating a functional configuration of theimage forming apparatus 100 of at least one embodiment. FIG. 3illustrates a part of the hardware configuration. The image formingapparatus 100 includes a control unit 60 (e.g., a controller), thedisplay 110, the control panel 120, a printer unit 130, the sheetaccommodating unit 140, the image reading device 150, a networkinterface 170, an auxiliary storage device 180, and a memory 190. Eachfunctional unit is connected so that data communication is possible viaa system bus 2.

The display 110, the control panel 120, the printer unit 130, the sheetaccommodating unit 140, and the image reading device 150 are the same asthose described above, and thus the description thereof will be omitted.Hereinafter, the control unit 60, the network interface 170, theauxiliary storage device 180, and the memory 190 will be described.

The control unit 60 is a processor such as a central processing unit(CPU) or a graphics processing unit (GPU). The control unit 60 controlsthe operation of each functional unit of the image forming apparatus100. The control unit 60 executes various processing by loading theprogram stored in the read only memory (ROM) into the random accessmemory (RAM) and executing the program. An application specificintegrated circuit (ASIC) may have an appropriate function realized bythe control unit 60. The ASIC is a dedicated circuit for realizing aspecific function.

Here, an example of the processing of the control unit 60 will bedescribed. If the control unit 164 provided in the image reading device150 notifies that there is a sheet, the control unit 60 instructs thecontrol unit 164 to start scanning. The control unit 60 notifies thecontrol unit 164 of the magnification information, the number of readinglines, the double-sided reading information, the information regardingthe presence and absence of the rear end streak cut, and the informationon the cut amount input from the control panel 120 (e.g., by a user) orthe like.

The control unit 60 includes a front-side image reading timer and aback-side image reading timer. The front-side image reading timer andthe back-side image reading timer are timers realized by software. Thefront-side image reading timer is a timer that measures the time duringwhich the image on the front side of the sheet is being read. Thecontrol unit 60 starts the front-side image reading timer at the timingwhen a front-side reading signal is obtained. The control unit 60 turnsoff the front-side sub-scanned image enabled signal at the timing whenthe time indicated by the front-side image reading timer elapses thetime corresponding to the number of reading lines.

The back-side image reading timer is a timer that measures the timeduring which the image on the back side of the sheet is being read. Thecontrol unit 60 starts the back-side image reading timer at the timingwhen a back-side reading signal is obtained. The control unit 60 turnsoff the back-side sub-scanned image enabled signal at the timing whenthe time indicated by the back-side image reading timer elapses the timecorresponding to the number of reading lines.

The network interface 170 sends and receives data to and from otherdevices. The network interface 170 operates as an input interface andreceives data transmitted from other devices. The network interface 170operates as an output interface and transmits data to other devices.

The auxiliary storage device 180 is, for example, a hard disk or a solidstate drive (SSD) and stores various data. The various data are, forexample, digital data, jobs, job logs, and the like. The digital data isdigital data of image information generated by the image reading device150.

The memory 190 is, for example, a random access memory (RAM). The memory190 temporarily stores data used by each functional unit of the imageforming apparatus 100. The memory 190 may store digital data generatedby the image reading device 150. The memory 190 may temporarily storejobs and job logs.

FIG. 4 is a timing chart (e.g., a timeline) illustrating the processingflow of the image forming apparatus 100 in at least one embodiment. Thecontrol unit 164 included in the image reading device 150 controls eachroller such as the pickup roller 155 according to the instruction tostart scanning, and conveys the sheet mounted on the mounting unit 151.The sheet conveyed to each roller is detected by the front-side readingstart sensor 158. For example, the front-side reading start sensor 158detects the front end of the conveyed sheet.

At the timing when the front end of the sheet reaches the front-sidereading start sensor 158, the control unit 164 starts the front-sidereading start timer and the sheet length measurement timer. When thefront-side reading start timer reaches the first conveyance time, thecontrol unit 164 notifies the control unit 60 of the image formingapparatus 100 of the front-side reading signal.

Upon receiving the front-side reading signal, the control unit 60 of theimage forming apparatus 100 turns on the front-side sub-scanned imageenabled signal and starts the front-side image reading timer. As aresult, the image in the sub-scan direction of the front side of thesheet is read from the timing when the front-side sub-scanned imageenabled signal is turned on. It is assumed that the sheet passes throughthe front-side reading position FRP and the front end of the sheet isdetected by the back-side reading start sensor 160.

At the timing when the front end of the sheet reaches the back-sidereading start sensor 160, the control unit 164 starts the back-sidereading start timer. When the back-side reading start timer reaches thesecond conveyance time, the control unit 164 notifies the control unit60 of the image forming apparatus 100 of the back-side reading signal.The waveform in the dotted circle 200 illustrated in FIG. 4 illustratesthe influence on the sensor output due to the fluttering of the rear endof the back side of the sheet.

The control unit 60 of the image forming apparatus 100 turns on theback-side sub-scanned image enabled signal and starts the back-sideimage reading timer in response to the reception of the back-sidereading signal. As a result, the image in the sub-scan direction of theback side of the sheet is read from the timing when the back-sidesub-scanned image enabled signal is turned on.

At the timing when the rear end of the sheet passes through thefront-side reading start sensor 158, the control unit 164 starts thefront-side reading end timer and stops the sheet length measurementtimer.

When the front-side reading end timer reaches the conveyance timecalculated based on the distance obtained by subtracting the value ofthe cut amount of the rear end streaks, which is obtained in advance,from the first conveyance distance, the control unit 164 sets to maskthe image data on the front side. As a result, the image data after thefront-side reading end timer reaches the conveyance time calculatedbased on the distance obtained by subtracting the value of the cutamount of the rear end streaks, which is obtained in advance, from thefirst conveyance distance is subject to mask processing. For example,the control unit 60 masks the image data on the front side from thetiming when the setting for masking the image data on the front side ismade. When the front-side image reading timer has elapsed a timecorresponding to the number of reading lines, the control unit 60 turnsoff the front-side sub-scanned image enabled signal.

When the back-side image reading timer reaches a value obtained bysubtracting the time corresponding to the cut amount of the rear endstreaks from the value indicated by the sheet length measurement timerobtained by the measurement of the front side, the control unit 60performs mask processing on the image data on the back surface. As aresult, the image data after the back-side image reading timer reachesthe value obtained by subtracting the time corresponding to the cutamount of the rear end streaks from the value indicated by the sheetlength measurement timer obtained by the measurement of the front sideis subject to mask processing. When the back-side image reading timerhas elapsed a time corresponding to the number of reading lines, whichis notified by the control unit 60, the control unit 164 instructs thecontrol unit 60 to turn off the back-side sub-scanned image enabledsignal. The control unit 60 turns off the back-side sub-scanned imageenabled signal.

According to the image forming apparatus 100 configured as describedabove, it is possible to stably read both sides of the sheet.Specifically, the image forming apparatus 100 performs mask processingon the rear end of the back-side sheet at the timing when the on-time ofthe front-side reading start sensor 158 elapses from the timing when theback-side reading start sensor 160 detects the sheet. That is, the imageforming apparatus 100 stops reading the image on the back side of thesheet at the timing when the on-time of the front-side reading startsensor 158 elapses from the timing when the back-side reading startsensor 160 detects the sheet. As a result, the influence on the sensordue to the fluttering of the rear end of the sheet can be reduced, andthe sheet can be read by the same length on both the front side and theback side. Therefore, both sides of the sheet can be read stably.

The image forming apparatus 100 receives an instruction input forenabling or disabling the mask processing via a control panel or thelike. This makes it possible to change whether or not to execute themask processing in response to the user's request.

A modified example of the image forming apparatus 100 will be described.In the above description, the image forming apparatus 100 that executesprinting by the image forming processing and the image fixing processinghas been described as an example. The above-mentioned processing may beapplied to the image reading device that reads an image without theimage forming apparatus 100 performing an image forming processing andan image fixing processing. In this case, the image reading device isprovided with the control unit 164. The control unit 164 performs boththe processing of the control unit 164 described above and theprocessing of the control unit 60.

A computer may realize some functions of the image forming apparatus 100in the above-described embodiment. In that case, a program for realizingthese functions is recorded on a computer-readable recording medium.Then, the functions may be realized by causing a computer system to readand execute a program recorded on a recording medium in which theabove-described program is recorded. The “computer system” referred tohere includes hardware such as an operating system and peripheralequipment. “Computer-readable recording medium” refers to a portablemedium, a storage device, or the like. The portable medium is a flexibledisk, magneto-optical disk, ROM, CD-ROM, or the like. The storage deviceis a hard disk built in the computer system or the like.

Further, the “computer-readable recording medium” dynamically holds aprogram for a short time, such as a communication line for transmittinga program via a communication line. The communication line is a networksuch as the Internet, a telephone line, or the like. The“computer-readable recording medium” may be a volatile memory inside acomputer system serving as a server or a client. The volatile memoryholds a program for a certain period of time. The above-describedprogram may be for realizing a part of the above-described functions.The above-described program may be realized by combining theabove-described functions with a program already recorded in thecomputer system.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of at least oneembodiments described herein may be made without departing from thespirit of the inventions. The accompanying claims and their equivalentsare intended to cover such forms or modifications as would fall withinthe scope and spirit of the inventions.

What is claimed is:
 1. An image reading device comprising: a trayconfigured to support a sheet; a paper feed roller positioned to conveythe sheet away from the tray; a first sensor positioned to detect afront end and a rear end of the sheet as the sheet is conveyed; a secondsensor positioned to detect the front end of the sheet as the sheet isconveyed; a scanner configured to read an image on a front side of thesheet at a front-side reading position and configured to read an imageon a back side of the sheet at a back-side reading position; and acontroller configured to: determine a first time duration that elapsesfrom the detection of the front end of the sheet by the first sensor tothe detection of the rear end of the sheet by the first sensor; andoperate the scanner to read the image on the back side of the sheet overa second time duration equal in length to the first time duration, thesecond time duration beginning at a first point in time after the frontend of the sheet is detected by the second sensor and ending at a secondpoint in time.
 2. The image reading device of claim 1, wherein thecontroller is configured to begin performing mask processing on theimage on the back side of the sheet at the second point in time.
 3. Theimage reading device of claim 2, further comprising: a control panelconfigured to accept an instruction input for enabling or disabling themask processing, wherein the controller is configured to perform themask processing in response to an indication that the mask processing isenabled.
 4. The image reading device of claim 1, wherein the controlleris configured to: start a front-side reading end timer when the rear endof the sheet is detected by the first sensor; end reading of the imageon the front side of the sheet based on the front-side reading endtimer; calculate a conveyance time based on a distance obtained bysubtracting (a) a cut amount of the sheet from (b) a conveyance distancefrom the first sensor to the front-side reading position; and beginperforming mask processing on the image on the front side of the sheetwhen the front-side reading end timer reaches the conveyance time. 5.The image reading device of claim 1, wherein the controller isconfigured to: receive a number of reading lines prior to reading theimage on the front side of the sheet and prior to reading the image onthe back side of the sheet; end reading of the image on the front sideof the sheet in response to the scanner having read the image on thefront side of the sheet for a first threshold length of time, the firstthreshold length of time corresponding to the number of reading lines;and end reading of the image on the back side of the sheet in responseto the scanner having read the image on the back side of the sheet for asecond threshold length of time, the second threshold length of timecorresponding to the number of reading lines.
 6. The image readingdevice of claim 5, wherein the first threshold length of time isequivalent to the second threshold length of time.
 7. The image readingdevice of claim 1, wherein the controller is configured to: start asheet length measurement timer when the front end of the sheet isdetected by the first sensor; stop the sheet length measurement timerwhen the rear end of the sheet is detected by the first sensor; anddetermine a length of the sheet based on a value of the sheet lengthmeasurement timer.
 8. The image reading device of claim 1, wherein thefirst sensor is an optical sensor, and the second sensor includes amovable portion.
 9. The image reading device of claim 8, wherein thesecond sensor detects the sheet in response to the sheet contacting themovable portion and driving movement of the movable portion.
 10. Theimage reading device of claim 1, further comprising: a first roller thatis provided between the first sensor and the front-side reading positionand configured to convey the sheet downstream; and a second roller thatis provided between the second sensor and the back-side reading positionand configured to convey the sheet downstream.
 11. An image readingmethod comprising: supporting, by a tray, a sheet; conveying, by a paperfeed roller, the sheet away from the tray; detecting, by a first sensor,a front end and a rear end of the sheet as the sheet is conveyed;detecting, by a second sensor, the front end of the sheet; determining afirst time duration that elapses from the detection of the front end ofthe sheet by the first sensor to the detection of the rear end of thesheet by the first sensor; reading, by a scanner, an image on the frontside of the sheet at a front-side reading position; and reading, by thescanner, an image on the back side of the sheet at a back surfacereading position over a second time duration equal in length to thefirst time duration, the second time duration beginning at a first pointin time after the front end of the sheet is detected by the secondsensor and ending at a second point in time.
 12. The image readingmethod of claim 11, further comprising performing, by a controller, maskprocessing on the image on the back side of the sheet at the secondpoint in time.
 13. The image reading method of claim 12, furthercomprising: receiving, by a control panel, an instruction to enable ordisable the mask processing, wherein performing the mask processing inresponse to the instruction enabling the mask processing.
 14. The imagereading method of claim 11, further comprising: starting, by acontroller, a front-side reading end timer when the rear end of thesheet is detected by the first sensor; ending reading of the image onthe front side of the sheet based on the front-side reading end timer;calculating, by the controller, a conveyance time based on a distanceobtained by subtracting (a) a cut amount of the sheet from (b) aconveyance distance from the first sensor to the front-side readingposition; and performing, by the controller, mask processing on theimage on the front side of the sheet when the front-side reading endtimer reaches the conveyance time.
 15. The image reading method of claim11, further comprising: acquiring a number of reading lines prior toreading the image on front side of the sheet and prior to reading theimage on the back side of the sheet; ending reading of the image on thefront side of the sheet in response to the scanner having read the imageon the front side of the sheet for a first threshold length of time, thefirst threshold length of time corresponding to the number of readinglines; and ending reading of the image on the back side of the sheet inresponse to the scanner having read the image on the back side of thesheet for a second threshold length of time, the second threshold lengthof time corresponding to the number of reading lines.
 16. The imagereading method of claim 11, further comprising: starting, by acontroller, a sheet length measurement timer when the front end of thesheet is detected by the first sensor; stopping, by the controller, thesheet length measurement timer when the rear end of the sheet isdetected by the first sensor; and determining, by the controller, alength of the sheet based on a value of the sheet length measurementtimer.
 17. The image reading method of claim 11, wherein the firstsensor is an optical sensor, and the second sensor includes a movableportion.
 18. The image reading method of claim 17, wherein the secondsensor detects the sheet in response to the sheet contacting the movableportion and driving movement of the movable portion.
 19. The imagereading method of claim 11, further comprising: conveying, by a firstroller, the sheet downstream, the first roller being provided betweenthe first sensor and the front-side reading position; and conveying, bya second roller, the sheet downstream, the second roller being providedbetween the second sensor and the back surface reading position.
 20. Animage reading device comprising: a tray configured to support a sheet; apaper feed roller positioned to convey the sheet away from the tray; asensor positioned to detect a front end and a rear end of the sheet asthe sheet is conveyed; a scanner configured to read an image on thesheet at a reading position; and a controller configured to: operate thescanner to begin reading the image on the sheet after the sensor detectsthe front end of the sheet; start a timer when the rear end of the sheetis detected by the sensor; end reading of the image on the sheet basedon the timer; calculate a conveyance time based on a distance obtainedby subtracting (a) a cut amount of the sheet from (b) a conveyancedistance from the sensor to the reading position; and begin performingmask processing on the image on the sheet when the timer reaches theconveyance time.